Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so the safety profile is covered. The description earns credit for two things beyond that: DST-aware expansion semantics and the per-call cost with the x402 payment scheme, which the agent must know about before invoking. It doesn't disclose occurrence limits or edge-case behavior when the range is exhausted, so it stops short of rich behavioral context.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two short sentences, front-loaded with the core capability and its vocabulary, followed by the one operational fact (price) an agent needs before calling. Nothing is repeated from the schema and nothing is wasted.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return values need not be explained, and pricing plus payment method are disclosed. However, for a recurring-date expander the practical failure modes (unbounded rules, the 200-occurrence cap, missing time zone defaults) are left entirely to the schema, so an agent must open the schema to call it confidently.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline would be 3. The description adds real meaning on top: it clarifies that expansion happens in a named time zone and is DST-aware, which explains how timezone and start interact, and it confirms excluded dates are supported as an optional refinement.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description pairs a precise verb ("Expand") with a precise resource ("an iCalendar RRULE") and illustrates it with examples like "every 2nd Tuesday." That is enough to separate it from date_add or date_diff, but it never distinguishes itself from the closest sibling, cron_schedule, which an agent could plausibly pick for the same recurring-expression task.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is implied by the input format: use this when you have an RRULE string and need concrete occurrences. There is no explicit when-not guidance, no instruction to prefer parse_date_text or cron_schedule for natural-language or cron expressions, and no note about what happens when the RRULE is malformed.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.